Method and system to determine distance using time of flight measurement comprising a control circuitry identifying which row of photosensitive image region has the captured image illumination stripe

Abstract

A time of flight sensor has an image region and a storage region on a device which may be a CCD. A pulse of light illuminates an object, and an image illumination stripe is recorded on the image region. In a distance determining step, the image region is clocked after emitting the pulse of light and the row in which the image illumination stripe is illuminated gives a measure of the distance to the object. The apparatus can self calibrated by emitting a pulse of light without clocking the image region.

The invention claimed is: 
     
       1. A time of flight distance measurement method comprising:
 emitting a pulsed fan beam from a light emitter to illuminate a remote object with an object illumination stripe ( 5 ); 
 capturing an image of the object illumination stripe as an image illumination stripe ( 15 ) on a photosensitive image region ( 8 ) of a time of flight sensor ( 9 ) comprising an array of M columns of J rows of pixels, where both M and J are positive integers greater than 2, 
 transferring data from the photosensitive image region ( 8 ) to a storage region ( 9 ) arranged not to respond to incident light, the storage region comprising M columns of N storage elements, along the M columns of the storage region from respective columns of the photosensitive image region; and 
 reading out data in a readout section ( 11 ) from the M columns of the storage region ( 2 ); the method comprising 
 operating a self-calibration step including capturing the image illumination stripe ( 15 ) on the photosensitive image region ( 8 ), then reading out the data from the image region ( 8 ) via the storage region ( 10 ) and the readout section ( 11 ) and identifying which row of the photosensitive image region has the image illumination stripe; and 
 operating a distance determining step including determining the distance to the remote object by clocking the image region ( 8 ) while capturing the image of the object illumination stripe ( 15 ), reading out the data from the image region ( 8 ) via the storage region ( 10 ) and the readout section ( 11 ) and determining the distance to the object. 
 
     
     
       2. A time of flight distance measurement method according to  claim 1 , comprising:
 driving the image region with static potentials during the self-calibration step. 
 
     
     
       3. A time of flight distance measurement method according to  claim 1 , wherein:
 the self-calibration step comprises: 
 not clocking the photosensitive image region ( 8 ) for a capturing period to capture an image of the image illumination stripe on the photosensive image region, then 
 clocking the image region ( 8 ), the storage region ( 10 ) and the readout region ( 11 ) to read out the captured image to identify the location of the image illumination stripe on the photosensitive image region ( 8 ); and 
 calibrating the location of the image illumination stripe. 
 
     
     
       4. A time of flight distance measurement method according to  claim 1 , comprising:
 determining that the image illumination stripe will be approximately in row Y; 
 applying (N+Y−K) clock cycles to the image region and storage region, where K is a positive integer at least 2; and 
 reading out 2K rows of the store section to determine the actual row Ya of the image illumination stripe. 
 
     
     
       5. A time of flight distance measurement method according to  claim 3 , wherein the method comprises controlling independently the clocking of the photosensitive image region, the storage region, and the readout section; the method comprising:
 clearing the image region, storage region and readout section; 
 emitting a first laser pulse; 
 capturing a first illumination image on the image region; 
 clocking the image region and storage region sufficiently to transfer the first illumination image to the storage region; 
 emitting a second laser pulse; 
 clocking the image region and the storage region at the predetermined clock frequency to capture a second illumination image and transfer it to the storage region; 
 clocking the readout section to readout the storage section and identify the number of rows between the first and second illumination image; and 
 determining the distance to the object from the number of rows between the first and second illumination image. 
 
     
     
       6. A time of flight distance measurement method according to  claim 1  further comprising:
 alternating the self-calibration step and the distance determining step. 
 
     
     
       7. A time of flight distance measurement method according to  claim 1  further comprising:
 carrying out a self-calibration step at less than 20% of the frequency of carrying out the distance determining step. 
 
     
     
       8. A time of flight distance measurement system, comprising:
 a light emitter ( 2 , 3 ) arranged to emit a pulsed fan beam for illuminating a remote object with a pulsed illumination stripe; 
 a time of flight sensor ( 9 ) comprising:
 a photosensitive image region ( 8 ) comprising an array of M columns of P rows of pixels, where both M and P are positive integers greater than 2, arranged to respond to light incident on the photosensitive image region ( 8 ); 
 a storage region ( 10 ) arranged not to respond to incident light, the storage region comprising M columns of N storage elements, arranged to transfer data along the M columns of storage from a respective one of the M pixels along column of N storage elements; and 
 a readout section ( 11 ) arranged to read out data from the M columns of the storage region; and 
 
 circuitry ( 1 ) for controlling the time of flight sensor ( 6 ) to capture image data of the pulsed illumination stripe along a row of pixels and to transfer the captured image data to the storage section; 
 wherein the circuitry is arranged to operate the time of flight sensor in a self-calibration step including capturing the image illumination stripe on the photosensitive image region ( 8 ), then reading out the data from the image region ( 8 ) via the storage region ( 10 ) and the readout section ( 11 ) and identifying which row of the photosensitive image region has the image illumination stripe; and 
 in a distance determining step including determining the distance to the remote object by clocking the image region while capturing the image of the object illumination stripe, reading out the data from the image region ( 8 ) via the storage region ( 10 ) and the readout section ( 11 ) and determining the distance to the object. 
 
     
     
       9. A time of flight distance measurement system according to  claim 8 , wherein the time of flight sensor is a charge coupled device. 
     
     
       10. A time of flight distance measurement system according to  claim 8 , wherein photons incident over at least 90% of the area of the photosensitive image region are captured by the photosensitive image region.